In knock controlled internal combustion engines (hereinafter "I.C. engines" or "ICE") it is important that the knock sensor is monitored for continued proper functioning, as a failure in the knock sensor gives rise to a danger that the ignition timing will shift toward premature ignition. In turn, premature ignition leads to functional disruptions and to the eventual destruction of the I.C. engine. Similarly, engine damage may occur if the knock control responds to the charge pressure of a supercharged I.C. engine.
It is known in the art that knocking may be substantially reduced by adjusting certain operating parameters under control. These parameters include the ignition timing or, as in the case of super or turbo-charged I.C. engines, the charge pressure.
These parameters are adjusted in a controlled manner only during certain engine operating conditions when knocking occurs. Such operating conditions include occurrence of engine revolutions (RPMs) higher then a predetermined threshold value when the ignition timing is not retarded soon enough, thus resulting in engine knock due to pre-ignition. In addition, engine knock may occur at elevated power requirements as is typical in super-charged I.C. engines. These methods of reducing engine knock in I.C. engines (by adjusting the ignition timing or charge pressure during knock-generating ranges) limit the ultimate performance of the engine. For the I.C. engine to remain operational under such controlled conditions, the I.C. engine must be operated well below its knock limit. Hence optimization of the I.C. engine's power and exhaust capabilities is compromised.
Another problem that arises under such operating conditions in conventional knock-controlled I.C. engines is the jump in torque that occurs in response to a sudden shift in the ignition timing when the operating mode of the I.C. engine goes from knock-free conditions into knock-susceptible ranges. Such a jump in torque is perceived by the driver as an unpleasant stall or a lurching movement as the I.C. engine is accelerated from low power or RPM ranges.
Other problems occur when a damaged knock sensor suddenly begins to work again. When the knock sensor becomes operational, the I.C. engine is reset from the controlled ignition timing setting to a controlled operation which is optimized near the knock boundary. As described above, an abrupt change in the operating condition of the I.C. engine occurs and is perceived as unpleasant by the driver due to the sudden change in ignition timing.
The prior art describes various methods to manipulate ignition timing in response to a failure of the knock sensor in order to eliminate knocking in knock-controlled I.C. engines. DE-A 34 45 177 discloses how to retard the ignition timing upon failure of the knock sensor through a corresponding fault-protection rectifier, in order to reliably avoid a knocking operation. This setting occurs jump-like to a fixed value.
DE-A 33 13 036 discloses how to create a knock control that allows incremental, step-like setting, but that is operated with faster control constants under sudden operating changes, such as occurs during accelerations.
Finally, DE-A 35 45 809 describes a knock control where a rough correction with fast ignition jumps is superimposed with a fine-tuned correction.
In practice it turns out that when monitoring knock sensors for failure, the response to such a failure is to adjust the operating parameter (ignition timing, charge pressure, etc ) to a fixed value which often results in very powerful jumps in torque (surges and stalls) that can result in driving mistakes. Thus, there is a definite need in the art to provide a method that incrementally shifts ignition timing in response to a failure in the knock sensor or a sudden reactivation of a previously failed knock sensor in knock-controlled internal combustion engines so that dramatic jumps in torque are avoided.